Use of block-copolymeric polyalkylene oxides as friction reducers in synthetic lubricants

ABSTRACT

The invention relates to the use of block copolymers containing at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups as friction-reducing additive and also compositions and lubricant formulations containing the block copolymers of the invention.

The present application claims priority from German Patent Application No. DE 10 2012 215 145.1 filed on Aug. 27, 2012, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the use of block copolymers containing at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups as friction-reducing additive and also compositions and lubricant formulations containing the block copolymers of the invention.

The invention thus relates to the use of block-copolymeric polyalkylene oxides obtained by alkoxylation as friction reducers in synthetic oils such as polyalkylene glycols which are used as lubricants. The lubricants can be used, inter alia, in gearboxes, bearings or engines.

It is noted that citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.

For the purposes of the present invention, lubricants are liquids which are intended to prevent direct contact of base body and counterbody. Formation of a lubricating film between two surfaces which move relative to one another reduces the friction, which can be measured by the coefficient of friction f. The coefficient of friction is defined as the ratio of the frictional force F_(R) and the normal force F_(N) (force perpendicular to the surface). This coefficient of friction, also referred to as frictional coefficient or traction coefficient, can be shown as a function of the speed of the moving surfaces, e.g. by means of a Stribeck curve (FIG. 1) (Wilfried J. Bartz, Additive für Schmierstoffe, 1994, 68-71). Depending on the conditions in the tribological system, various frictional and lubrication states occur. If the molecules of the lubricant are completely displaced at contact points formed between two surfaces, limit friction prevails. The friction is then very high and leads to damage to the surfaces. If at least a few molecules of the lubricant separate the base body from the counterbody at the roughness peaks of the surfaces, the friction decreases dramatically, and this is referred to as mixed friction. In the case of liquid friction, often also referred to as hydrodynamic lubrication, a liquid film separates the surfaces. In integrated terms, friction and wear are lowest in the region of liquid friction. An important parameter is the release point, which characterizes the commencement of mixed friction as the speed decreases. Base body and counterbody should where possible be operated under liquid friction as a result of suitable lubricants. The lower the viscosity can be made, the more energy-efficient is the apparatus, which can be, for example, a gearbox.

In the prior art, additives which can maintain the lubricant film in this state of liquid friction as long as possible, i.e. even at high engagement forces F_(N) on the counterbody, are added to lubricants. Such additives act, for example, by film formation at the surface of the metal parts, by physical and/or chemical adsorption and prevent metallic contact between the sliding partners (Wilfried J. Bartz, Additive für Schmierstoffe, 1994, 53-54).

It is noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like; and that terms such as “consisting essentially of” and “consists essentially of” have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.

It is further noted that the invention does not intend to encompass within the scope of the invention any previously disclosed product, process of making the product or method of using the product, which meets the written description and enablement requirements of the USPTO (35 U.S.C. 112, first paragraph) or the EPO (Article 83 of the EPC), such that applicant(s) reserve the right to disclaim, and hereby disclose a disclaimer of, any previously described product, method of making the product, or process of using the product.

Synthetic lubricants within the meaning of the present invention contain, for example, polyalkylene glycols, esterols, adipates. The advantages of synthetic lubricants compared to mineral oil-based lubricants are, for example, the possibility of tailoring viscometric properties by means of a targeted synthesis. Further advantages are the often very good low-temperature properties and also polarity produced by, for example, ether or ester groups which results in an affinity with metal surfaces and thus can more readily ensure an intact lubricating film, even under load, than the completely nonpolar mineral oils. However, like all base oils based on mineral oil, the synthetic lubricants also have weaknesses in the region of mixed or limit friction under increasing load or relatively high temperature, which can be measured by a higher coefficient of friction. An increasing temperature results in a decrease in the viscosity. It is therefore necessary to find a compromise between low viscosity and acceptable lubricating film thickness when formulating lubricating oils.

Lubricants should firstly have sufficiently high viscosities at high temperatures to maintain lubricating films which do not detach and to reduce wear. Secondly, very low viscosities at low temperatures are desirable to reduce the energy input by minimizing the liquid friction.

The friction and in the case of excessively high load the wear of the sliding partners is reduced by addition of conventional lubricant additives to the base oils. The combination of base oil and additives gives the lubricant. Since the viscosity is a decisive criterion for lubricants, lubricants are divided into ISO-VG classes (viscosity class in accordance with DIN 51519). Here, the viscosity indicated is the kinemetic viscosity at 40° C. The designation ISO-VG 320 thus means that the lubricant has a viscosity of 320 mm²/s at 40° C. Additives which are used as friction reducers or for wear protection are, for example, fatty acid esters, phosphoric esters, triaryl phosphates or sulphur compounds such as organic polysulfides, thioesters, thiadiazoles. Additive packets which frequently contain, for example, amine-based corrosion inhibitors in addition to the wear protection additives are frequently also used. Disadvantages of the prior art are that, in particular at temperatures of >70° C. as frequently occur in the lubrication gap, the abovementioned reduction in the viscosity occurs and the lubricating film breaks, which results in contact and thus wear of the mostly metallic surfaces.

Present-day additives have an only unsatisfactory effect at high temperatures, particularly in synthetic oils, because, commercial additives have been conceived for use in base oils based on mineral oil. A further disadvantage of these poorly matched combinations of additive and base oil is that the tribological system goes into the mixed friction region even under mild conditions, which allows the friction to increase greatly. Countermeasures employed hitherto are the use of oils having a higher viscosity in order to, for example, increase the lubricating film thickness and thus the load-bearing capability, but this results in a poorer energy efficiency. Furthermore, many of these friction reducers contain ecologically problematical additives such as sulphur compounds.

It is therefore an object of the present invention to overcome at least one disadvantage of the prior art.

Block copolymers which satisfy the criteria of one of the claims of the present invention are surprisingly able to achieve this object.

SUMMARY OF THE INVENTION

The present invention accordingly provides for the use of block copolymers containing at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups as friction-reducing additive.

The present invention further provides compositions which contain at least one block copolymer which contains at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups together with at least one antioxidant.

The invention further provides lubricant formulations containing block copolymers which contain a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups in a synthetic base oil or synthetic lubricant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic depiction of a Stribeck curve. The traction coefficient or coefficient of friction is plotted against the speed.

FIGS. 2 a and b: Measurement principle of the mini traction machine.

FIGS. 3 to 10: Stribeck curves as per Example 3 with the parameters Fn=30 N, SRR=50%, temperatures 33° C. (diamonds), 70° C. (squares), 88° C. (triangles) indicated there.

FIG. 3: Stribeck curves of the base oil ISO VG 46: Polyalkylene glycol of the viscosity class ISO VG-46 with a viscosity index of 196, without additives, blanks.

FIG. 4: Stribeck curves of the formulation SF 6 as per Example 2.

FIG. 5: Stribeck curves of the formulation SF 1 as per Example 2.

FIG. 6: Stribeck curves of the formulation SF 4 as per Example 2.

FIG. 7: Stribeck curves of the formulation SF 5 as per Example 2.

FIG. 8: Stribeck curves of the formulation SF 3 (not according to the invention) as per Example 2.

FIG. 9: Stribeck curves of the base oil ISO VG-32, TMA, blanks.

FIG. 10: Stribeck curves of the formulation SF 2 as per Example 2. The present invention will now be described in detail on the basis of exemplary embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements which are conventional in this art. Those of ordinary skill in the art will recognize that other elements are desirable for implementing the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein.

The block copolymers for the use preferably contain a block of aromatic oxyalkylene groups having more than one, preferably from 2 to 9, more preferably from 2 to 8, particularly preferably more than 2 to less than 4, aromatic oxyalkylene groups. The block copolymers for the use also preferably contain a block of nonaromatic oxyalkylene groups having from 2 to 50, preferably from 5 to 25, particularly preferably from 8 to 15, nonaromatic oxyalkylene groups. The block copolymers for the use particularly preferably contain a block of aromatic oxyalkylene groups having more than one aromatic oxyalkylene group and at least one block of nonaromatic oxyalkylene groups having more than 2 nonaromatic oxyalkylene groups.

Further preference is given to the use of block copolymers of the formula (1).

R¹[O(AO)_(g)(NAO)_(h)R²]_(n)  Formula (1)

where

-   n is from 1 to 8, preferably from 1 to 4, more preferably 1 or 2, in     particular 1, -   g is greater than or equal to from 1 to 9, preferably from 2 to 8,     particularly preferably from greater than 2 to less than 4, -   h is greater than or equal to from 3 to 50, preferably from 4 to 20,     in particular from 5 to 13, -   the radicals R¹ are each, independently of one another, a     straight-chain or branched or cycloaliphatic hydrocarbon radical     having from 1 to 18 carbon atoms, preferably from 2 to 14 carbon     atoms, more preferably from 3 to 10 carbon atoms, in particular 8     carbon atoms, -   the radicals R² are each, independently of one another, hydrogen, an     alkyl radical having from 1 to 8 carbon atoms, preferably from 1 to     4 carbon atoms, in particular methyl, or an acyl radical having from     2 to 12 carbon atoms, -   the radicals AO are, independently of one another, aromatic     oxyalkylene groups, -   the radicals NAO are, independently of one another, nonaromatic     oxyalkylene groups, -   as friction-reducing additive.

Preference is given to block copolymers for the use which contain at least one oxystyrene-containing group as aromatic oxyalkylene group.

The nonaromatic oxyalkylene groups are more preferably oxyethylene, oxypropylene and/or oxybutylene.

Further preference is given to the use of block copolymers of the formula (2)

R¹[O(SO)_(a)(EO)_(b)(PO)_(c)(BO)_(d)R²]_(n)  Formula (2)

where

-   SO is oxystyrene, -   EO is oxyethylene, -   PO is oxypropylene, -   BO is oxybutylene and -   a is from greater than 1 to 9, preferably from 2 to 8, particularly     preferably from greater than 2 to less than 4, -   b is from 1 to 20, preferably from greater than 1 to 18, more     preferably from 2 to 15, in particular from greater than 2 to 13, -   c is from 0 to 20, from greater than 0 to 15, more preferably from 1     to 10, in particular from greater than 1 to 6, -   d is from 0 to 10, preferably from 0 to 5, more preferably from 0 to     2, in particular 0 or 1,     as friction-reducing additive.

Preference is given to the use according to the invention of polyalkylene oxides in which the sum of the indices a, b, c and d is equal to or greater than from 3 to 59, preferably from 6 to 35, more preferably from 10 to 20. Further preference is given to polyalkylene oxides in which the proportion of oxyethylene radicals is from at least 25 to 90 mol %, preferably from at least 30 to 80 mol %, in particular from 35 to 77 mol %, based on the sum of the alkylene oxides used.

When c and d are each 0, the value of b is greater than or equal to three times the value of a.

Particular preference is given to blockwise arrangements in which the radical R¹ is followed by a block containing at least one aromatic oxyalkylene group and then a block containing at least one nonaromatic oxyalkylene group. Very particular preference is given to blockwise arrangements in which the radical R¹ is followed by a block containing, on statistical average, from 2.8 to 3.2 units of oxystyrene.

The indices reproduced here and the value ranges of the indices indicated can be understood as average values of the possible statistical distribution of the structures actually present and/or mixtures thereof. This also applies to structural formulae which themselves are reproduced precisely, for example the formulae (1) and (2).

The alkoxylation products of the formula (1) for the use are preferably colourless to yellow-orange products which can be clear or opaque.

For the purposes of the present invention, the term polyether encompasses both polyethers, polyetherols, polyalkylene oxides and also polyether alcohols, which may be used synonymously with one another. The expression “poly” does not necessarily indicate that a plurality of ether functions or alcohol functions are present in the molecule or polymer. Rather, the expression merely indicates that at least repeating units of individual monomer building blocks or else compositions which have a higher molar mass and also a certain polydispersity are present.

The word fragment “poly” encompasses, for the purposes of the present invention, not only exclusively compounds having at least 3 repeating units of one or more monomers in the molecule, but in particular also compositions of compounds which have a molecular weight distribution and an average molecular weight of at least 300 g/mol. This definition takes account of the fact that it is customary in the field of industry in question to refer to such compounds as polymers even if they do not appear to conform to a polymer definition analogous to the OECD or REACH guidelines.

The oxyalkylene groups described by the indices b, c and d in the formulae (1) and (2) can have any statistical distribution in the polymer chain. Statistical distributions can be made up of blocks with any number of blocks and any sequence or can have a randomized distribution; they can also be incorporated alternately or else form a gradient over the chain. In particular, they can also form all mixed forms in which groups having different distributions may follow one another.

The compatibility with the base oil can be adjusted by means of the indices b, c and d. A person skilled in the art will be familiar with the fact that the compounds are present in the form of a mixture having a distribution governed essentially by statistical laws. The hydrophobicity/hydrophilicity balance can be specifically controlled via the various alkylene oxide monomers and their proportion in the total polymer in such a way that the compatibility with the respective base oil can be adapted in a targeted manner.

The radical R¹ is the hydrocarbon radical of an alcohol having 1 or up to 8, preferably from 1 to 4, more preferably 1 or 2 and in particular 1, hydroxyl group(s). At the beginning of the polymerization, the alcohol of the formula R¹—O—H reacts with the loss of the terminal proton. Preferred alcohols are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, cyclopropylmethanol, 1-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 1-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2,2-dimethyl-1-butanol, 3,3-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, 1-heptanol, 1-octanol, 2-ethyl-1-octanol. A particularly preferred alcohol is 1-octanol.

Preferred radicals R² are hydrogen and/or alkyl radicals having from 1 to 8 carbon atoms and/or acyl radicals having from 2 to 12 carbon atoms, where the alkyl and acyl radicals can be linear, branched or cyclic. Preferred alkyl radicals are methyl, ethyl, n-propyl or n-butyl, with particular preference being given to methyl. Preferred acyl radicals are acetyl, propionyl or 2-ethyhexanoyl.

Particularly preferred block copolymers for the use, polyalkylene oxides containing oxystyrene groups, have radicals R¹=n-octyl and R²=hydrogen.

Particularly preferred block copolymers of the formula (2) for the use are:

a): octyl —(SO)₃-(EO)₁₀—H b): octyl —(SO)₃—(PO)_(5,5)-(EO)_(5,5)—H where SO, EO and PO are as defined above.

Without wishing to be tied to this theory, it can be presumed that the delocalized electrons of the aromatic ring of the oxystyrene units are responsible for the adsorption of the molecule on the metal surface.

The block copolymers for the use can be prepared by methods known in the prior art. However, preference is given to using block copolymers prepared using base catalysis, the preparation of which is described in principle in EP1078946 (U.S. Pat. No. 6,552,091). These documents, in particular the preparative methods, are fully incorporated by reference into the present invention.

The above-mentioned documents emphasize the importance of the starting alcohol (paragraph 30 of U.S. Pat. No. 6,552,091). This can, apart from the abovementioned definitions of R¹, preferably be selected from among natural fatty alcohols or synthetic fatty alcohols. The natural fatty alcohols are preferably selected from among mixtures of C₁₆/C₁₈- or C₁₂/C₁₄-alcohols. Particularly preferred natural fatty alcohols are straight-chain n-alcohols. The synthetic fatty alcohols are preferably selected from among C₉/C₁₁- or C₁₃/C₁₅-alcohols. Particularly preferred synthetic fatty alcohols are branched-chain alcohols. Particular preference is given to alcohols whose hydroxyl group is primary, i.e. terminal.

The basically produced block copolymers which have been neutralized by means of acids are preferably used according to the invention. The acids are preferably organic acids. Particularly preferred organic acids are, for example: formic acid, acetic acid, propionic acid, butyric acid, valeric acid, adipic acid, octanoic acid, 2-ethylhexanoic acid, lactic acid, gamma-hydroxybutyric acid, malic acid, citric acid, ascorbic acid, trifluoromethane sulfonic acid, benzoic acid and the hydroxyl-containing derivatives such as para-hydroxybenzoic acid and salicylic acid. Particular preference is given to the use according to the invention of block copolymers which have not been neutralized by means of inorganic acids, in particular not by means of inorganic acids such as hydrohalic acids, e.g. HCl, phosphoric acids or phosphonic acids such as H₃PO₄, ethylphosphonic acid, sulphuric acid or sulfonic acids such as H₂SO₄, methylsulfonic acid, ethylsulfonic acid. A person skilled in the art will know of analogous inorganic acids having different oxidation states of the central atoms of the acid, e.g. phosphinic acids.

The block copolymers for the use preferably contain metal ions.

Preferred metal ions are those of the group consisting of the alkali metals and the alkaline earth metals, with particularly preferred ions being those of sodium, potassium and calcium, in particular of potassium.

The metal ions present can originate from the polymerization reaction or the neutralization by means of an acid with salt formation in the preparation of the block copolymers for the use, but they can also have been added subsequently in the form of salts. Preferred salts are the alkali metal or alkaline earth metal salts of the abovementioned acids. Particular preference is given to the salts of lactic acid, in particular sodium, potassium or calcium lactate, with a special preference being given to potassium lactate.

The block copolymers for the use preferably contain at least 500 ppm of metal ions, preferably more than 1500 ppm, more preferably more than 2500 ppm, particularly preferably more than or equal to 3000 ppm, based on the mass of the block copolymers.

Apart from the abovementioned metal ions, further metal, semimetal, transition metal or noble metal ions can be present. These further metal ions may also have a synergistic effect in respect of reducing the friction. These further metal ions can optionally be present in a content close to the detection limit, based on the amount of the block copolymers.

The block copolymers for the use can optionally contain an excess of acid. Various acids can also have been added at the same time or in succession.

If for the purposes of the present invention, reference is made to natural materials, e.g. lactate, or chiral compounds such as ethylhexanoic acid, this is basically intended to include all stereoisomers; preference is given to the naturally occurring isomers in each case, here in the cited case of lactate, L-lactate. For the definition of natural materials, reference may be made to the full scope of the “Dictionary of Natural Products”, Chapman and Hall/CRC Press, Taylor and Francis Group, e.g. in the on-line version of 2011: http://dnp.chemnetbase.com/.

Particularly preferred block copolymers of the formula (2) for the use are those of the structures a) and b) prepared using lactic acid.

Terminally etherified polyalkylene oxides can, for example, be obtained under the conditions of the Williamson ether synthesis according to the prior art by reaction of the hydroxyl-terminated polyether with aliphatic, straight-chain or branched alkyl halides. The reaction with methyl chloride is preferred. In this way, the hydroxyl end groups can be either partially or completely etherified.

Terminally esterified compounds can be obtained according to the prior art by reaction of the hydroxyl-terminated polyethers with carboxylic acids and/or carboxylic anhydrides and/or carboxylic acid halides, optionally with addition of catalysts. Preference is given to the esters of acetic acid or of 2-ethylhexanoic acid. In this way, the hydroxyl end groups can be either partially or completely esterified.

The present invention further provides compositions as friction-reducing additive containing block copolymers of the formulae (1) or (2) which contain a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups together with at least one antioxidant.

Preference is given to compositions according to the invention which contain at least 500 ppm of metal ions, preferably more than 1500 ppm, more preferably more than 2500 ppm, particularly preferably more than or equal to 3000 ppm, based on the mass of the block copolymer used.

Antioxidants, also referred to as antioxidatives, can be, for example, derivatives of 2,4-di-tert-butylphenol and also corresponding esters such as phosphonites or phosphites; further antioxidants can also be esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Examples of antioxidatives are the series Irganox® and Irganox® DW (trademark of BASF: Irganox L 06, Irganox L 57, Irganox L 64, Irganox L 74, Irganox L 101, Irganox L 107, Irganox L 109, Irganox L 115, Irganox L 135, Irganox L 150), the series Irgafos® (trademark of BASF: e.g. Irgafos 168 (CA RN 31570-04-4), Irgafos 126, Irgafos XP 60, Irgafos XP 30, Irgafos OPH, Irgafos P-EPQ (CA RN 119345-01-6)).

An advantageous use according to the invention can be use of the composition according to the invention as friction-reducing additive. Preferred compositions according to the invention comprise further additives such as extreme pressure/antiwear additives (ep/aw additives), corrosion inhibitors, biocides, defoamers, dispersants, metal deactivators or viscosity index improvers in addition to block copolymers of the formula (1) or (2) and antioxidants. Such compositions can be referred to as additive packets.

Preferred lubricant formulations according to the invention contain synthetic base oils or synthetic lubricants, in particular polyalkylene glycols (PAG) such as PAG ISO VG 46, esterols such as TMP (trimethylolpropane esters) and adipates such as TMA (trimethyl adipate), e.g. TMA ISO VG 32.

Preferred lubricant formulations according to the invention can contain other additives customary in the prior art, e.g. antioxidatives, corrosion inhibitors, defoamers, dispersants, viscosity index improvers, biocides, metal deactivators or extreme pressure/antiwear additives, in addition to block copolymers for the use containing at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups and the base oil.

The further additives in the compositions of the invention and the formulations of the invention can have a synergistic effect in respect of the friction-reducing effect. In particular, synergistic effects are to be expected when ep/aw additives, metal deactivators or viscosity index improvers are added.

Extreme pressure/antiwear additives are also referred to as ep/aw additives. They can be, for example, phosphates or thiophosphates.

The block copolymers for the use are present in preferred lubricant formulations according to the invention in a concentration of 0.1-9 percent by weight (% by weight) added to base oils; preference is given to the use of 0.3-3% by weight, particularly preferably 0.5-1% by weight, based on the total lubricant formulation.

It can be advantageous for the lubricant formulations of the invention to contain further friction reducers.

Recording of the Stribeck curves can be carried out as described in the prior art. For the purposes of the present invention, the dependence of the traction values on the speed is determined by means of a “mini traction machine” from PCS Instruments. The way in which the measurements are carried out is described in the examples. The examples are hereby fully incorporated by reference. Traction coefficients under the conditions described of more than 0.095 cause visible damage to the measurement system, the ball and/or the plate.

Advantageous lubricants thus have a friction-reducing effect. This friction-reducing effect is the lowering of the Stribeck curves over the region shown in the figures compared to the base oil as blank. Furthermore, a friction-reducing effect can be characterized by a very large speed range below a traction coefficient of 0.095. A likewise advantageous sign of a friction-reducing effect can be a lower release speed compared to the corresponding base oil as blank. Friction-reducing effects are particularly advantageously characterized by a flat Stribeck curve below a traction coefficient of 0.095.

The block copolymers for the use, the compositions of the invention, their use and the lubricants of the invention are described by way of example below without the invention being restricted to these illustrative embodiments. Where ranges, general formulae or classes of compounds are indicated below, these are intended to encompass not only the respective ranges or groups of compounds which are explicitly mentioned but also all subranges and subgroups of compounds which can be obtained by leaving out individual values (ranges) or compounds. Where documents are cited in the present description, the contents thereof are fully incorporated by reference into the disclosure content of the present invention. If contents (ppm or %) are indicated below or above, these are, unless indicated otherwise, % by weight or ppm by weight In the case of compositions, the contents indicated are, unless indicated otherwise, based on the total composition. When averages are mentioned below, these are, unless indicated otherwise, number averages. If molar masses are referred to, these are, unless expressly stated otherwise, weight average molar masses Mw. If, in the context of the present invention, values for viscosities are indicated, these are, unless stated otherwise, dynamic viscosities which can be determined by methods with which a person skilled in the art will be familiar. When measured values are indicated below, these measured values were, unless indicated otherwise, determined at a pressure of 1013.25 hPa and a temperature of 25° C.

OPERATIVE EXAMPLES Example 1 Synthesis of the Polyalkylene Oxides for the Use S1a (Preparation of a Polyether of Octanol-(SO)₃-(EO)₁₀):

130.2 g of 1-octanol and 5.25 g of potassium methoxide were placed in a 3 litre autoclave. The reactor was made inert by evacuation and flushing with nitrogen. The content of the reactor was heated to 115° C. while stirring. 388 g of styrene oxide were added at an internal temperature of 115° C. over a period of half an hour. After an after-reaction time of 2 hours at 115° C., 473 g of ethylene oxide were added continuously over a period of 2 hours. The reaction temperature was maintained at 115° C. by cooling. The internal pressure in the reactor in this phase was not more than 3.5 bar (absolute). After an after-reaction time of 1 hour, still at 115° C., the reaction was complete, indicated by no further decrease in the internal pressure. The internal temperature in the reactor was reduced to 90° C. by cooling, and volatile constituents were subsequently removed by degassing under reduced pressure. The product obtained was neutralized by means of lactic acid (90% by weight in water) and the water was removed by vacuum distillation. The polyether was subsequently filtered and dispensed. The product is a clear, yellow-orange liquid having an OH number of 68.4 mg KOH/g and an acid number of 0.1 mg KOH/g.

The product S1b was prepared in a manner analogous to S1a, but was neutralized by means of acetic acid.

The product S1c was prepared in a manner analogous to S1a, but was neutralized by means of phosphoric acid.

S2 (Preparation of a Polyether of Octanol-(SO)₃-(EO)_(5.5)—(PO)_(5.5)):

130.2 g of 1-octanol and 5.25 g of potassium methoxide were placed in a 3 litre autoclave. The reactor is made inert by evacuation and flushing with nitrogen. The content of the reactor was heated to 115° C. while stirring. 388 g of styrene oxide were added at an internal temperature of 115° C. over a period of half an hour. After an after-reaction time of 2 hours at 115° C., a mixture of 261 g of ethylene oxide and 344 g of propylene oxide was added continuously over a period of 135 minutes. The reaction temperature was maintained at 115° C. by cooling. The internal pressure in the reactor in this phase was not more than 3.5 bar (absolute). After an after-reaction time of 1.5 hours, still at 115° C., the reaction was complete, indicated by no further decrease in the internal pressure. The internal temperature in the reactor was reduced to 90° C. by cooling, and volatile constituents were subsequently removed by degassing under reduced pressure. The product obtained was neutralized by means of lactic acid (90% by weight in water) and the water was removed by vacuum distillation. The polyether was subsequently filtered and dispensed. The product is a clear, yellow-orange liquid having an OH number of 64.8 mg KOH/g and an acid number of 0.2 mg KOH/g.

Example 2 Lubricant Formulations

The formulations were produced by simple mixing at room temperature.

A polyalkylene glycol of the viscosity class ISO VG-46 having a viscosity index of 196 (this will hereinafter be referred to as base oil ISO VGT 46) and a trimethyl adipate (TMA) are used as base oils. The TMA is admixed with an additive packet containing 4.5% by mass of a viscosity index improver based on PMA (a polymethacrylate-based substance) and an ep/aw additive from Infineum having the designation P 666 (it is known in the prior art that the amount of ep/aw additive is about 0.3% by weight); this mixture corresponds to an oil of the viscosity class ISO-VG 32 and has a viscosity index of 230.

For comparative purposes, Na-Lube AW 6220 (a phosphorus- and nitrogen-containing additive formulation for use as friction reducer in industrial lubricants from King Industries) was used as commercial friction reducer.

TABLE 1 Lubricant formulations (SF) as per Example 2 using the block copolymers as per Example 1 as additive ISOVG-46 ISO VG-32 plus 1% by weight plus 0.5% by weight Additive of additive of additive S 1a SF 1 S 1b SF 4 S 1c SF 5 S 2 SF 6 SF 2 Na-Lube SF 3

Example 3 Use Tests

When surfaces sliding over one another, e.g. the tooth flanks of toothed wheels, are no longer separated by a lubricant film, the surfaces of the sliding partners come into contact with one another. The result is mechanical, adhesive wear. Antiwear additives then reduce the friction and in the worst case the surfaces which come into contact with one another are welded together as a result of formation of surface layers having a lower shear strength than in the case of the pure metals. The additive according to the invention is adsorbed on the metal surface under relatively mild conditions and under high stresses in the mixed friction region it significantly reduces the friction compared to the pure base oil to which no additive has been added. This mode of action can be depicted in a Stribeck curve (FIG. 1). The Stribeck curve depicts the course of the frictional force in a coordinate system. The coefficient of friction is shown on the abscissa, and the function of speed, pressure and viscosity is shown on the ordinate.

Recording of Stribeck Curves:

The Stribeck curves were recorded using a mini traction machine from PCS Instruments (measurement principle shown in FIGS. 2 a and 2 b). The tribological contact is established by a polished ball having a diameter of 19.05 mm and made of a chromium-containing steel (100 Cr 6: AlSi 52100, DIN 1.3505) and a polished disc having a diameter of 46 mm and made of the same material as the ball. Ball and disc are driven independently of one another and thus produce a sliding/rolling contact. The test liquid was introduced into the test reservoir. The program automatically went through the indicated loads, speeds, slide-roll ratios and temperatures.

The Stribeck curve was produced at a load F_(N) of 30 N, corresponding to a Hertz pressure of 0.93 GPa. The lubricant temperature was set to 33° C., 70° C. and 88° C. The fixed slide-roll ratio (SRR) was set to 0.5 (50%), defined as the ratio of sliding friction in %, which is defined as (v_(disc)−v_(ball))/v_(average))*100% (v=speed), with the speed (mean speed) having been varied in the range from 2000 mm/s-5 mm/s 10 values were recorded at each temperature, 5 starting at a low speed and 5 starting at a high speed. The average was calculated from the 10 measured values by determination of the median.

As blanks, the respective base oils ISO VG 46 and ISO VG 32 were measured.

The release speeds can be determined graphically by fitting a straight line to the linear region at relatively high speeds. The corresponding speeds can then be taken from the measured values.

In this way, the following release speeds were determined:

TABLE 2 Release speeds in [mm/s] as per Example 3 for the lubricant formulations as per Example 2, using the base oil ISO VG 46 Blank SF 6 SF 1 SF 4 SF 5 SF 3 FIG. 3 FIG. 4 FIG. 5 FIG. 6 FIG. 7 FIG. 8 70° C. 500 150 120 150 200 250 88° C. >1000 250 100 400 400 600

Result of Example 3:

TABLE 3 Speeds in [mm/s] at which visible damage to the disc or ball of the Mini Traction Machine were observed ISO VG-46 ISO VG-32 Blank SF 6 SF 1 SF 4 SF 5 SF 3 Blank SF 2 33° C. 11 <5 <5 8 6 5 <5 <5 70° C. 26 <5 <5 <5 <5 5 13 <5 88° C. 33 <5 <5 <5 10 15 15 <5

The coefficient of friction using polyalkylene glycol (ISO VG 46) was significantly reduced by addition of 1% by weight of the additives for the use. In the mixed friction region at speeds of the test specimens of <100 mm/s, coefficient of friction of >0.1, which under the present test conditions means visible scratches on the metal surface of the test specimens, are achieved in the case of the oil to which no additive has been added. Especially at elevated temperature above 70° C., which can be normal temperatures at the contact surface in gearboxes, the viscosity becomes so low that very high coefficients of friction are measured. However, this is reduced significantly by the additives for the use as per Example 1 (S1a, S1b, S1c). The commercial product NA-Lube used for comparative purposes reduces the coefficient of friction less significantly.

The use according to the invention of block copolymers containing a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups as friction-reducing additive leads to a significant reduction in the coefficients of friction in the mixed friction and limit friction regions. This prevents or reduces wear. Furthermore, the block copolymers for the use make it possible for processes to be carried out more energy-efficiently. The use of low-viscosity base oils can also be expanded by means of the block copolymers for the use in the region of higher loads.

While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the inventions as defined in the following claims. 

1. A method of using a block copolymer containing at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups as a friction-reducing additive.
 2. The method according to claim 1, wherein the block copolymer contains at least one block of aromatic oxyalkylene groups having more than one aromatic oxyalkylene group and at least one block of nonaromatic oxyalkylene groups having more than 2 nonaromatic oxyalkylene groups.
 3. The method according to claim 1, wherein the block copolymer is a compound of formula (1) R¹[O(AO)_(g)(NAO)_(h)R²]_(n)  Formula (1) where n is from 1 to 8, g is greater than or equal to from 1 to 9, h is greater than or equal to from 3 to 50, R¹ is a straight-chain or branched or cycloaliphatic hydrocarbon radical having from 1 to 15 carbon atoms, R² is hydrogen or an alkyl radical having from 1 to 8 carbon atoms, AO independently of one another, aromatic oxyalkylene groups, NAO independently of one another, nonaromatic oxyalkylene groups.
 4. The method according to claim 1, wherein the block copolymer is a compound of formula (2) R¹[O(SO)_(a)(EO)_(b)(PO)_(c)(BO)_(d)R²]_(a1)  Formula (2) where a1 is from 1 to 8, R¹ is a straight-chain or branched or cycloaliphatic hydrocarbon radical having from 1 to 15 carbon atoms, R² is hydrogen or an alkyl radical having from 1 to 8 carbon atoms, SO is oxystyrene, EO is oxyethylene, PO is oxypropylene, BO is oxybutylene and a is from 1 to 9, b is from 1 to 20, c is from 0 to 20, d is from 0 to
 10. 5. A composition of at least one block copolymer containing at least a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups together with at least one antioxidant.
 6. The composition according to claim 5, wherein the composition contains at least 500 ppm of metal ions, based on the mass of the block copolymers used.
 7. A method of using the block copolymers according to claim 1 for producing lubricant formulations.
 8. A lubricant formulation containing block copolymers which contain a block of aromatic oxyalkylene groups and a block of nonaromatic oxyalkylene groups in a synthetic base oil or synthetic lubricant.
 9. The lubricant formulation according to claim 8, further comprising additives selected from the group consisting of synthetic oils, extreme pressure/antiwear additives (ep/aw additives), corrosion inhibitors, biocides, defoamers, dispersants, metal deactivators or viscosity index improvers.
 10. The lubricant formulations according to claim 8, wherein the block copolymers are used in a concentration of 0.1-9% by weight, based on the total lubricant formulation.
 11. The lubricant formulations according to claim 8, wherein the synthetic oils are polyalkylene glycols. 